A main circuit of this type of power conversion device has a converter which converts AC voltage from an AC power supply to DC voltage and supplies the DC voltage to a DC link section including a smoothing capacitor, and an inverter which converts the DC voltage of the DC link section to AC voltage in a variable-voltage variable-frequency manner and supplies the AC voltage to an AC motor which is an AC load. When the power conversion device is connected to the AC power supply, an LC resonance circuit is formed by an inductance component L which the AC power supply has and the capacitor C of the DC link section.
It is known that, when three-phase AC voltage is rectified by a converter having diodes, oscillation having a frequency six times as large as a power supply frequency occurs on the DC output side. Therefore, when the resonance frequency of the LC resonance circuit coincides with the frequency six times as large as the power supply frequency, voltage of the DC link section in the power conversion device greatly oscillates. As a result, a main circuit component might be broken or control for the AC motor might become unstable.
In particular, in the case of using a capacitor having a small capacitance as the smoothing capacitor, there is a high possibility that the LC resonance phenomenon occurs.
In this regard, for example, Patent Document 1 proposes technique for suppressing occurrence of overvoltage due to the resonance phenomenon. That is, Patent Document 1 discloses, in FIG. 15, a method for suppressing oscillation of voltage of the DC link section in a power conversion device that drives a synchronous motor by vector control.
Specifically, voltage of the DC link section is detected, an AC component is extracted from the detected voltage, and a q-axis voltage command is corrected by a signal obtained by multiplying the AC component by a gain K.
Thus, it is allegedly possible to prevent a phenomenon in which voltage of the DC link section greatly oscillates and overvoltage occurs.